1. Field of the Invention
The present invention relates to a real-image finder optical system, and in particular, relates to a diopter adjustment mechanism.
2. Description of the Related Art
In a compact camera (for example), a real-image finder optical system has the own optical axis which is separate from the optical axis of the photographing optical system. The real-image finder optical system includes a positive objective optical system which forms an object's inverted image which is upside down and reversed from left to right, an erecting optical system which erects the inverted image to the same orientation as the object, and a positive eyepiece optical system through which the erected image is viewed.
In a real-image finder optical system of this type, diopter adjustment is conventionally carried out by moving the eyepiece lens element along the optical axis thereof. In such a diopter adjusting mechanism in which the position of the eyepiece lens element is adjusted, there is an advantage of not increasing the number of lens elements. However, since a space is required in order to move the eyepiece lens element along the optical axis thereof, the thickness of the camera body has to be increased. Alternatively, if the camera body is made small and thin, a space to allow the eyepiece lens element to move cannot be secured, and thereby the diopter adjusting range cannot be made large.